The influence of charge on nuclear magnetic resonance isotope effects

1987 ◽  
Vol 65 (12) ◽  
pp. 2707-2712 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Neil Burford
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Isoelectronic Series ◽  
Deuterium Isotope Effects ◽  
Charged Ions ◽  
Nuclear Magnetic

Deuterium isotope effects on the 31P shielding constants and spin–spin coupling constants in the isoelectronic series, PH2−, PH3, PH4+, are examined. Also, deuterium isotope effects on the nuclear magnetic resonance parameters of SnH3− are examined and compared with our earlier results on SnH4 and SnH3+. The experimental results are analyzed using the models of Jameson and Osten. In each isoelectronic series it is found that the isotope effects on the heavy atom chemical shifts are largest for the negatively charged ions and essentially zero for the positively charged ions, as predicted by recent molecular orbital calculations. The primary isotope effects on J(A,H) are positive for all species containing lone-pair electrons, otherwise Δp1J(A,H) is negative. The primary and secondary isotope effects on J(Sn,H) in the SnH3− ion are the largest reported to date.

13C nuclear magnetic resonance spectra of 3,6-disubstituted pyridazines

1991 ◽  
Vol 69 (6) ◽  
pp. 972-977 ◽  
Author(s):  
Gottfried Heinisch ◽  
Wolfgang Holzer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13C nuclear magnetic resonance spectra of 17 3,6-disubstituted pyridazine derivatives have been systematically analyzed. Chemical shifts and various 13C, 1H coupling constants are reported. Attempts were made to correlate these data with results obtained from semiempirical molecular orbital calculations as well as with substituent electronegativities and Taft's substituent constants σI and σR0. Key words: 3,6-disubstituted pyridazines, 13C NMR spectroscopy, 13C, 1H spin coupling constants.

Molecular orbital calculations and 1H nuclear magnetic resonance spectra as indicators of internal rotational potentials in some methyl derivatives of styrene

1988 ◽  
Vol 66 (4) ◽  
pp. 584-590 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Carbon Carbon Bond ◽  
Nuclear Magnetic Resonance Spectra ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 1H nuclear magnetic resonance spectra of the α-methyl, cis and trans-β-methyl, 4-methyl, and β,β-dimethyl styrènes are analyzed to yield long-range proton–proton coupling constants. With the assumptin that the internal rotational potential for styrene in the gas phase is unaltered in solution, a consistent treatment of over 40 of the long-range coupling constants is given in terms of the known coupling mechanisms. Expectation values of sin2 θ, where θ is the angle of twist about the exocyclic carbon–carbon bond, are presented for these molecules. These are compared with theoretical potentials at the 6-31 G level of molecular orbital theory. The present data indicate rather larger average twist angles than those in the literature. The extrema (at θ = θ° and 90°) in the angle dependent long-range coupling constants appear to be rather smaller in magnitude than are theoretical values obtained from valence bond and molecular orbital approaches.

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